The parable of the fig tree found in these verses is the last parable that Jesus tells in the Gospel of Luke. This parable is found also in Mark 13,28-29 and Matthew 24,32-33, but whereas Mark and Matthew speak only of the fig tree, Luke speaks of “the fig tree and all the trees” (21,29). When people can see for themselves that these trees have come out in leaf they know for themselves that summer is near, so when they see the Son of Man coming in a cloud (21,27) they will know that the kingdom is near. Since Luke probably thought that the end would come soon, he has added the last two sayings about what will not pass away until “these things” have taken place. They are “this generation” and the “words” of Jesus. These pronouncements must serve as a reminder of the assurance of redemption for the believer.
Our job as Christians is not to bother about when the end will be but to live fully in the present moment. If we do so then no matter when the end comes we will always be ready.